Project Summary We address important knowledge gaps involving how changes in marijuana policy affect adolescents, especially the effectiveness of these policies at attending to longstanding racial disparities. We will investigate how changes in marijuana policy affect marijuana possession arrests, which can have life- long negative consequences. We will also identify states where policy change could be related to disparities in marijuana use. To our knowledge, neither of these topics has been covered in the academic literature. Our primary goal is to assess how the timing of the implementation of medical marijuana laws, marijuana decriminalization, and marijuana legalization are related to changes in: (1) race-based differences in adolescent marijuana use within states over time, (2) adolescent marijuana possession arrest rates, and (3) the disparity between Black and White adolescent marijuana possession arrests. For comparison, we will also assess how these policies have affected adult arrests and rates of use, since they typically target adult use specifically. While the focus of the study is on longstanding racial disparities, we will also explore differences by sex. We will compare states that have implemented one of these marijuana policies to a ?synthetic control? state constructed from outcomes and covariates from states without a policy. This data-driven modeling procedure creates a synthetic counterfactual that is not limited by confounding introduced by changes over time that might occur in unexposed control states. This will allow us to focus on specific policy environments, which vary widely by state. In Aim 1 we examine whether state-level medical marijuana, marijuana legalization and marijuana decriminalization policies have led to an overall decline in adolescent arrests for marijuana possession. We hypothesize that changes in marijuana policy have been associated with an overall decline in adolescent marijuana possession arrests. In Aim 2 we determine whether there are differences in adolescent marijuana possession arrests based on race and sex. We hypothesize that White male and female adolescents have benefitted disproportionately from any decrease in marijuana possession arrests related to a change in marijuana policy. In Aim 3 we investigate whether differences in adolescent marijuana use at the state level account for any arrest disparities. We hypothesize that any disparities in marijuana possession arrests can be explained by between-groups differences in marijuana use. We will also explore apparent differences in marijuana use disparities within states over time and note obvious relationships between marijuana policy implementation and adolescent marijuana use disparities.